1. Field of the Invention
This invention relates to display apparatus, and more particularly to a raster scan display provided with line smoothing means for smoothing out stair-step effects inherent in the raster display of line segments.
2. Description of the Prior Art
The display apparatus concerned here is the kind having a display area which is effectively a regular array of display elements on which a symbol is produced by brightening selected ones of the display elements. One example of such a display apparatus includes a cathode ray tube arranged to be line-scanned in a television-type raster with digital control of display element brightness. However, other forms of display apparatus are known; for example, an array of light-emitting diodes arranged to be scanned electronically.
One disadvantage of such display is that, due to the discrete nature of the display elements, some symbol lines, e.g., those at a large or small angle to the raster lines in a line scan raster-type display, tend to suffer from the so-called "stairstep" effect, that is, instead of the line having a clean staight edge, it has a stepped appearance resembling the treads and risers of a staircase.
It is, therefore, a principle object of the present invention to overcome the disadvantages attendant in the prior art approaches and to provide improved apparatus for smoothing out stair-step effects inherent in the raster display of line segments.